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  1. Core Server
  2. SERVER-20495

MapReduceResult.find() and drop() error when outputting to a different DB

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    • Type: Icon: Bug Bug
    • Resolution: Done
    • Priority: Icon: Major - P3 Major - P3
    • None
    • Affects Version/s: 3.1.8
    • Component/s: MapReduce, Shell
    • Labels:
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      t = db.mr;
t.drop();

t.save( { x : 1 , tags : [ "a" , "b" ] } );
t.save( { x : 2 , tags : [ "b" , "c" ] } );
t.save( { x : 3 , tags : [ "c" , "a" ] } );
t.save( { x : 4 , tags : [ "b" , "c" ] } );

m = function(){
    this.tags.forEach(
        function(z){
            emit( z , { count : 1 } );
        }
    );
};

r = function( key , values ){
    var total = 0;
    for ( var i=0; i<values.length; i++ ){
        total += values[i].count;
    }
    return { count : total };
};

res = t.mapReduce(m , r , {out : { replace: "outColl", db: "outDb" } });
outDB.outColl.find().count()
res.find().count() // error, no results
      Show
      t = db.mr; t.drop(); t.save( { x : 1 , tags : [ "a" , "b" ] } ); t.save( { x : 2 , tags : [ "b" , "c" ] } ); t.save( { x : 3 , tags : [ "c" , "a" ] } ); t.save( { x : 4 , tags : [ "b" , "c" ] } ); m = function(){ this .tags.forEach( function(z){ emit( z , { count : 1 } ); } ); }; r = function( key , values ){ var total = 0; for ( var i=0; i<values.length; i++ ){ total += values[i].count; } return { count : total }; }; res = t.mapReduce(m , r , {out : { replace: "outColl" , db: "outDb" } }); outDB.outColl.find().count() res.find().count() // error, no results

      DBCollection's mapreduce function returns a MapReduceResult object, which takes in the result of db.runCommand(mapreduce).

      If the output is to a different db (i.e. when the "out" parameter is specified with an action instead of a collection name), the result is an object instead of a collection name string.

      This is passed into MapReduceResult and stored as the collection name, which in this case gets parsed as the string "[object BSON]". This variable is used by MapReduceResult.find() and MapReduceResult.drop().

      The two functions are not documented so maybe they could be cleaned up a bit.

            Assignee:
            robert.guo@mongodb.com Robert Guo (Inactive)
            Reporter:
            robert.guo@mongodb.com Robert Guo (Inactive)
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              Created:
              Updated:
              Resolved: